The present invention relates to the fabrication of data storage media, and more particularly to processes and devices for accurately characterizing the surfaces of rigid disk media.
Disk drives typically employ one or more rotatable disks in combination with transducers supported for generally radial movement relative to the disks. Each transducer is maintained spaced apart from its associated disk, at a "flying height" governed by an air bearing caused by disk rotation. Present day transducer flying heights typically range from about 25 nm to about 50 nm, and experience velocities (relative to the disk, due to disk rotation) in the range of 5-15 m/sec. Effective recording and reading of data depend in part upon maintaining the desired transducer/disk spacing. Flaws or discontinuities in an otherwise planar disk surface can interfere with reading and recording, and present a risk of damage to the transducer, the disk recording surface, or both. The continuing increase in data recording density in disk drives leads to more stringent requirements as to disk surface planarity, requiring improved manufacturing techniques to ensure that the number and size distribution of flaws or discontinuities remain below increasingly strict thresholds.
A critical aspect of rigid disk media manufacturing is the quality of substrates, upon which various magnetic thin films are to be deposited. Flaws in the substrate surface tend to be replicated by subsequent thin film layers, to become flaws in the finished product. Performance testing, i.e. in a disk drive or other typical usage environment, is not possible until after thin film layers have been applied to the substrate to provide the desired transducer flying height and glide characteristics. Destructive testing is unsatisfactory, and any visual inspection is difficult, because of the need to recognize potentially damaging flaws in the two micrometer range.
Therefore, it is an object of the present invention to provide a device for scanning the surface of a data recording medium, to more rapidly locate surface discontinuities and more accurately characterize a profile of each discontinuity.
Another object is to provide a method for scanning data storage media for surface flaws and other discontinuities in a non-contact, non-destructive manner usable at various stages of media fabrication.
A further object is to provide a surface scanning process and device employing a more selective approach to data acquisition, to more accurately characterize the profiles of surface discontinuities while avoiding unduly burdensome data storage requirements.
Yet another object is to provide a device using coherent energy in a non-contact scanning of the surface of a data recording medium, to more effectively optimize focusing of the coherent energy during scanning.